The present invention relates to a printed circuit board (PCB) with a built-in passive device, which is buried within the PCB, to a method for manufacturing the PCB, and to an elemental board for the PCB.
Multilayer PCBs in which semiconductor devices or electrical devices such as a capacitor and a resistor are buried are proposed to increase the device density and reduce the dimensions of the PCBs.
For example, JP-A-11-312868 discloses that kind of multilayer PCB. In the publication, a multilayer PCB is manufactured as follows. First, a plurality of insulating layers are formed. Each insulating layer includes a thermosetting resin film in B stage, or unhardened state. Each resin film has via-holes and wiring patterns. Then, the insulating layers and a resin film that includes an electrical device are stacked to form a stacked body. After that, the stacked body is heated to harden the thermosetting resin films, and a multilayer PCB with a built-in electrical device is completed.
Specifically, in the publication, for example, a capacitor is built in a multilayer PCB as follows. First, copper films are formed by plating on both sides of a polyimide film that has a glass transition temperature above the curing temperature of thermosetting resin films of insulating layers at a later step. Then, the copper films are patterned into predetermined shapes to form film-shaped capacitors. The polyimide film with the film-shaped capacitors is aligned with and placed on one of the insulating layers, and the polyimide film and the insulating layers are stacked for forming a stacked body. The stacked body is heat pressed to complete the multilayer PCB with a built-in capacitor.
In the method of the publication, insulating layers and a resin film that includes an electrical device are stacked, so the electrical device needs to be formed before the stacking. As a result, extra manufacturing steps are required for forming the electrical devices beforehand, and the multilayer PCB of the publication may be overly complex. In addition, the electrical device needs to be formed using a film that has high thermal resistance enough to remain intact at the hardening temperature of the thermosetting resin films of the insulating layers. Therefore, the materials that can be used for the thermosetting resin films are limited.